- Adult skin wounds normally heal with compromised tensile strength, loss of hair and gland structures, and possibly disfiguring scars. In contrast, fetal skin wounds heal without scarring by a tissue regeneration process. One of the major goals of wound healing research is to identify the factors which facilitate scarless fetal wound healing in order to someday achieve this process in adult wounds. The principal investigator entered the field of wound research with the hypothesis that developmentally regulated homeobox genes inform normal skin formation; and thus they provide signals which mediate scarless fetal wound regeneration. They also hypothesized that candidate fetal regeneration genes would normally be down-regulated in adult skin resulting in the loss of scarless wound healing capability. They took the approach of using molecular methods to clone developmentally important skin genes which might play a role in wound healing. They have cloned two new homeobox genes (PRX-2 and HOXB13) from regenerating wounded human fetal skin which met criteria for influencing fetal skin regeneration. PRX-2 was expressed in developing human fetal dermis, was down-regulated in adult skin, strongly expressed in cultured fetal fibroblasts, and was markedly upregulated in the dermis during scarless wound healing. In contrast, in normal adult skin PRX-2 was weakly expressed in the epidermis, and in adult wounded skin this epidermal signal was mildly increase but no signal was detected in the dermis. HOXB13 expression was detected in fetal dermis but was absent from adult dermis, was the strongest homeobox gene signal detected in regenerating wounded human fetal tissue, and HOXB13 expression decreased during fetal wound repair. This proposal describes experiments to test the role(s) of these two genes in normal skin development and wound healing: 1) They will define the PRX-2 and HOXB13 developmental expression patterns in normal mouse and human skin and in a murine in vivo fetal wound healing model; 2) use cultured fibroblasts either over- or under-expressing PRX-2 or HOXB13, to study their role(s) in cellular proliferation, regulation of growth factor and/or adhesion, or extracellular matrix protein gene expression, or capacity for in vitro wound healing; and 3) they will use PRX-2 and HOXB13 transgenic mice and PRX-2 knockout mice to test the roles of these genes during fetal and adult wound healing. They hope these data will, in the long term, permit a type of scarless wound healing in adult tissue.